A board of audit overseeing the Fukushima disaster is urging TEPCO to sue some of their contractors over failed projects. They specifically cited the frozen wall project, an early cesium adsorption filter system and the bolt together tanks. This may become interesting as there have been some informal accusations that TEPCO pressured contractors to cut corners on projects.

The Areva cesium filtration system cost $270 million USD, it was only in operation for 3 month and treated a small fraction of the water.
Machines from GE, Toshiba and Areva to remove salt from contaminated water all failed at the task. One only operated for 5 days, the longest was 6 weeks. Total cost, $150 million USD.
The leaking bolt together tanks cost $134 million USD and all have to be replaced.
The underground ponds cost $18 million USD. At one point the contractor had disputed accusations of their work being poor, claiming TEPCO insisted on downgraded materials.
Trench freezing that later had to be concreted in cost $840,000 USD.

Interest and financial costs funded by the state to TEPCO have also been drastically revised upwards. A combination of larger expenses, longer payback time frames and TEPCO’s continued under-performance financially is causing the state stake in resolving the disaster to grow. Much of the repayment plan had been based on an assumption that TEPCO would restart their Kashiwazaki Kariwa nuclear plant and use funds from that to help fund disaster work. With that plant still offline, the plan is seeing those strains.